The lack of satisfactory brightness is often a concern for electrophoretic display devices. Total internal reflection would occur with electrophoretic display devices due to the fact that the display device usually has components of a high refractive index. Because of the components having a higher refractive index (e.g., about 1.5) than the air (which has a refractive index of about 1) surrounding the display panel, some of the scattering light from the display panel may reflect back to the display device by total internal reflection. This total internal reflection phenomenon could result in a loss of about 30-50% of the scattering light, thus causing reduction in brightness.
A luminance enhancement structure can be used to enhance the brightness of an electrophoretic display. However, when a luminance enhancement structure is applied onto an electrophoretic display, the Moiré effect may occur which could significantly affect the quality of the images displayed. The Moiré effect may be avoided by designing different luminance enhancement structures for different display devices, depending on the size and shape of the display cells of the display device. In other words, depending on the size and shape of its display cells (or other equivalent repeated patterns, such as active matrix backplane), each display device has to have a customized luminance enhancement structure to avoid the Moiré effect. Such an approach obviously is not desirable because it could be costly.